This means that if LP Turbines are used for cooling buildings in hot arid climates a surplus of electricity will be produced.

Some of this electricity could be used for pumping sea water inland where additional LP Turbines could be used to power out of town freeze desalination plants. These plants would cool sea water to below 0oC so that ice was frozen out as fresh water. The ice could be transported back into town and allowed to melt in covered troughs above head height, along the busier streets of the town.

In principle, this method of purifying water could meet all of humanities domestic, industrial and agricultural needs if LP Turbines were used to provide the electricity, to drive the reverse osmosis pumps.

However, there are some niche markets where LP Turbines could be used in other ways, to produce drinking water.

The first niche relates to environments where even contaminated water is a scarce resource. The second relates to circumstances where the recovery of solids from the contaminated water is economically worthwhile.

Their unique feature: They convert heat into electricity. But unlike existing commercial heat engines they imitate nature by running cold. This allows them to extract heat from the air or oceans, or any other source of very low grade heat.

Until 1697, when the Dutch explorer Willem de Vlamingh discovered black swans in Australia, Europeans believed that all swans were white.

The philosopher Karl Popper used this discovery to support his argument that just because all of the evidence we can find supports a theory, this does not prove that the theory is absolutely correct. At some date in the future, we may find a new piece of evidence that contradicts the theory.

But engineers and scientists can't live their professional lives in constant doubt. So if a theory works for us time and again, we are quite entitled to use it.